1. Field of the Invention
The present invention relates to an active material for a high-capacity sodium ion battery.
2. Description of Related Art
Sodium ion batteries are batteries in which Na ions move between a positive electrode and a negative electrode. Since Na is more abundant than Li, sodium ion batteries have an advantageous effect in that the cost can be easily reduced as compared to lithium ion batteries. In general, a sodium ion battery includes: a positive electrode active material layer containing a positive electrode active material; a negative electrode active material layer containing a negative electrode active material; and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer.
The negative electrode active material used in the sodium ion battery has been actively studied. For example, International Publication WO 2013/042706 discloses an organic compound having a phenalenyl structure or a derivative thereof as an active material for a lithium ion battery. In addition, Japanese Patent Application Publication No. 2009-129742 (JP 2009-129742 A) describes that a cyclic compound is used as a negative electrode active material for a sodium ion secondary battery. Further, Japanese Patent Application Publication No. 2007-227186 (JP 2007-227186 A) discloses an organic compound having a phenalenyl structure as an active material not for a sodium ion battery but for a lithium ion battery.
International Publication WO 2013/042706 reports that Br3-trioxotriangulene or (t-butyl)3-trioxotriangulene having a phenalenyl structure functions as an active material for a lithium ion battery. However, it is neither known nor reported that an organic compound having a phenalenyl structure or a derivative thereof functions as an active material for a sodium ion battery.
In addition, reported examples of the active material for a sodium ion battery are fewer than those of the active material for a lithium ion battery. Therefore, an active material for a sodium ion battery having a crucial characteristic has yet to be developed.